In applying single or plural component sealants or adhesives on an assembly line or via a robot, remotely operated valves (pneumatic or electric) with a fluid "snuff-back" feature are often utilized. The snuff-back feature reverses the fluid flow at the nozzle slightly when the valve is closed to prevent dripping or stringing of the fluid being dispensed.
Commercially available snuff-back valves utilize a spool-type valve which runs in and out of a plastic "u" cup seal. In such a design, the shaft of the spool leaves and re-enters the seal in every valve cycle causing the seal to wear very quickly.